92 Steam-Engine Indicator. 



nary friction existed, which had for many months previous pre- 

 vented the engine from attaining its proper speed. 



In the first experiments we found, when the whole work was in 

 motion at the usual velocity, that the average pressure upon 

 each square inch of the piston amounted to 11.7 lbs., or about 

 l-3d more than it ought to have been; and that at this time 

 the engine, which is of forty-five horse power, made at Soho, 

 exerted a power, including its own friction, of more than 70 

 horses. Finding, in repeated trieils with detached parts of the 

 work, that the same extraordinary absorption pervaded every 

 department, we became convinced that the effect was produced 

 by some generally existing cause, and naturally directed our 

 attention to the quality of the oil which was in use throughout 

 the work. At one time we were in the habit of using that 

 which is known under the name of neat-foot, but owing to its 

 scarcity, and the extreme cheapness of rape oil, we began, 

 about two years ago, to mix with the former a small portion of 

 the latter. No apparent difference being discovered by the 

 workmen, this proportion was gradually increased, until the 

 stock of neat-foot oil being at last consumed, the rape oil be- 

 came the sole anti-attrition. And so gradually had the change 

 been effected, that the workmen even to the last denied the 

 existence of any unusual friction, and attributed the want of 

 speed solely to some defect in the engine, which daily exhibited 

 stronger symptoms of being overloaded. At length the use of 

 the rape oil was suspended, and spermaceti substituted ; and 

 in twenty-four hours the average pressure was reduced to 9.5 

 lbs. ; in a week after it had fallen to 9.1. At this time a mix- 

 lure of one-third sperm, and two-thirds rape oil was given out 

 to the workmen, and the friction, after the first day, gradually 

 increased, until at the end of a fortnight the average pressure 

 became 11.1 lbs. A return to the pure sperm oil again re- 

 duced the pressure to 9.5. Subsequent observations have given 

 from 8.7 to 9.6,but the inconstant motion of the machinery in a 

 cotton mill must at all times produce such a difference. 



